Solid-state lighting (SSL) technologies are used in a wide variety of lighting applications. As SSL technologies improve in areas such as energy efficiency, cost, and lifespan, such technologies represent viable alternatives to conventional lighting technologies in general illumination and display applications. One example of an SSL technology is semiconductor light-emitting diodes (LEDs). Semiconductor LEDs are used in various electronic, display and lighting applications. For example, display screens on devices such as televisions, monitors, and cell phones may use LED-backlit displays.
Nitride-based LEDs are one example LED type. Nitride LED improvements have focused on increasing light extraction rather than improving light generation efficiency. Flip-chip configurations of nitride LEDs have become widely used. In flip-chip configurations, light is emitted through the substrate on which the LED structures are grown. Light generation in flip-chip configurations, however, is not limited to a specific direction. Therefore, in order to increase light output, techniques for reflecting light emitted from the substrate in a desired direction are typically used.
Semiconductor LEDs typically emit light in all directions, with only a fraction of the emitted light escaping the LED package. To combat this loss, various packaging designs may be used. For example, in 5 mm LED packages in single diode applications, a reflector can be mounted or positioned to reflect light in a desired direction. Reflectors are particularly advantageous when used in conjunction with an LED package comprising a sapphire substrate. Sapphire substrates are transparent, and thus do not absorb the wavelength of interest for photons traversing the LED structure. The bottom of the sapphire substrate may be thinned by polishing to facilitate breaking of the wafer into LED chips and to eliminate absorption at the otherwise rough surface.
Various other techniques can be used to improve the output light efficiency of LED structures. For example, patterned sapphire substrates may be used. Another technique involves using patterned buried layers in the LED structure, as disclosed in U.S. patent application Ser. No. 13/617,169, filed Sep. 14, 2012 and entitled “Semiconductor Structure with Patterned Buried Layer,” which is commonly assigned herewith and incorporated by reference herein.